Replace std::map<K, V*> with std::map<K, std::unique_ptr<V>> to handle...

Replace std::map<K, V*> with std::map<K, std::unique_ptr<V>> to handle ownership and deletion of the values.

Ideally we would store the MultiClasses by value directly in the maps, but I had some trouble with that before and this at least fixes the leak.

llvm-svn: 223997